DX does not give you 1.5x magnification

[kirbinster]

Please correct me if I am mistaken, but I keep reading people say that their 300mm lens gives them more reach, equivalent to a 450mm lens on a DX body. My understanding is this is totally false. When you use a crop body your field of view is smaller thus the field of view is the equivalent of 1.5 times less than what you would get with a full frame camera, but there is no magnification. What you get is equivalent to taking the picture on the full frame body and then cropping away the outer one-third of the picture. Nothing actually gets magnified.

[PowerPix]

Mmmm, not sure on that whole comment. Where crop suffers is in the wide angle department.

Well, you might actually be right. Crop sensor I guess would just magnify the image making it appear to reach farther. No actual reach is aquired, maybe I'M just confused. lol

*ahem*

Crop Factor Explained

[vandergus]

Correct magnification is the same. For example, a macro lens that goes to 1:1 magnification on a full frame camera will still give you 1:1 magnification on a cropped sensor. There is a slight advantage, though, with pixel density, depending on the cameras you're comparing. Say you're trying to choose between a D3 and a D300, both 12 MP but the D3 is a full frame camera and the D300 a DX camera. And let's say that your trying to take a picture of a buffalo way off over the prairie. The D300 will give you more pixels on the eye lashes of that buffalo than the D3.

But this is really more of a pixel density thing than a crop factor thing, even though they are often confused.

[Chip]

If someone is referring to a "crop factor" and they speak in terms of "apparent magnification" or "effective focal length," then that's accurate. Because while the actual magnification remains the same, the cropping makes the magnification appear greater.

At least that's how I understand it.

[kirbinster]

I think that is saying the same thing that I said. If you take a picture with a 300mm lens on a full frame camera and then crop away one-third of it you get the same image as you took with the 300mm lens on the DX camera. This has to do with the field of veiw, there is no magnification of the lens.

[LoveDSLR]

How about 12 MP D3 + 450mm = 12 MP D3 + 300mm + ((1.5x)) = 12 MP D300 + 300mm image?

[gturner]

Originally Posted by kirbinster

Please correct me if I am mistaken, but I keep reading people say that their 300mm lens gives them more reach, equivalent to a 450mm lens on a DX body. My understanding is this is totally false. When you use a crop body your field of view is smaller thus the field of view is the equivalent of 1.5 times less than what you would get with a full frame camera, but there is no magnification. What you get is equivalent to taking the picture on the full frame body and then cropping away the outer one-third of the picture. Nothing actually gets magnified.

Try the exercise yourself as you answered your own question. The crop effect automatically brings the image closer (same size final canvas with a smaller area of picture)

It is not true magnification as the lens is still the same lens, but the EFFECTIVE FOCAL LENGTH of the final image gives the same FRAMING as a longer lens on a full frame camera.

[jeff.amadon]

It's all semantics. You're right, "magnification" isn't the truly correct word but the effect is the same (I think). If you had a 450mm lens on a 12MP full frame body you would get the same shot in the frame as a 300mm lens on a 12MP DX body. If you crop the full-frame shot, you reduce the pixel count, so to restore it you'd have to resize, in essence "magnifying" digitally.

I could be totally wrong but this is what I tell myself.

[sk66]

It is "effective" or "apparent" focal length.

Example my D3 and D300 and my 500mm lens:
The 500mm is 500mm regardless of what it's on.
The cameras are both 12MP.
The D300 sensor is smaller so it only captures the center area of the 500mm field of view at 12MP resolution. The D3 captures the entire view. To get the same image from both I have to crop down the D3 image resulting in approximately an 8MP image.

The cropping is not that big a difference as the D3 sensor has larger photosites so it does a better job per site in capturing data...That 8MP crop has almost the same "data" as the 12MP D300 image, but will suffer more with enlargement. (this is IME, not necessarily technically correct)

Or I can go to a 750mm lens on the D3 to capture the same "smaller FOV" the D300 captures with the 500mm giving me the best of both.


Now if you take a 24MP FF camera and crop the 500mm image back to what the D300 saw, the resulting image will be the same or better. You'd probably end up with something like a 15MP image...
But pixel density/size has significant other affects. So, for me, the low light performance and higher clarity (that's probably not technically correct) made the FF 12mp advantageous over a 24MP full frame.